Biochemical mechanisms determining the tissue-specific restriction of DNA in chromatin will be studied. Isolated chromatin from cells producing specific, definable protein species (plasma cell tumor, choriocarcinoma) will be used as a template for in vitro RNA synthesis. The RNA produced will be assayed by DNA-RNA hybridization and by its ability to serve as a messenger for the in vitro biosynthesis of specific proteins. Chromatin will be dissociated and the isolated dissociate fractions reconstituted to the DNA. The reconstituted chromatin will be used for in vitro RNA synthesis and the specificity of the RNA produced will be assayed. The elimination of various chromatin components or their substitution by similar fraction from other tissues should lead to the detection of specific regulatory molecules. It is most likely that these are nonhistone proteins. The nonhistone chromatin proteins will be fractionated and analyzed. Their specific interactions with DNA will be studied. Additionally, the contribution of the individual proteins of chromatin to its structure and conformation will be investigated using election microscopy and other techniques. Studies on the immunochemical properties of the nonhistone proteins of chromatin and their complexes with DNA will greatly aid the detection of tissue-specific regulatory proteins.